Restoration of catalyst by surface grinding



Dec. 15, 1964 J. w. PAYNE 3,160,998

RESTORATION OF CATALYST BY SURFACE GRINDING Original Filed Nov. 9, 19595 Sheets-Sheet i REA 670R 25 REGENERA 70/? INVENTOR.

- J0hn 14/ P0 U6 BY 2/ Affomey L/FTPOT Dec. 15, 1964 J. w. PAYNE3,160,998

RESTORATION OF CATALYST BY SURFACE GRINDING Original Filed Nov. 9, 19593 Sheets-Sheet 2 F/GZ F/GZ

iNVENTOR.

BY John 14 Payne Qua QFF Dec. 15, 1964 J. w. PAYNE RESTORATION 0FCATALYST BY SURFACE GRINDING 5 Sheets-Sheet 3 Original Filed Nov. 9,1959 John W Payne BY QM (Nip A f/omey United States Patent l 3,l6,998TESTGRATTGN QATALY SURIFAQE GETNMNG dehn W. 'iayne, Weotlhury, Null, togaeeuy Mobil Gil Eompany, line, a corporation of New York Griginalapplication Nov. 1950, Ser. No. 851,870, new Patent No. 3,050,117, datedGet. 23, B62. Divided and this application Feb. 3, 1962, er. No. 172,0214 Ciaims. (Cl. Bib-313) This invention relates to catalytic crackingsystems in which a cracking catalyst is contacted with hydracarbons toeffect conversion and is particularly concerned with maintaining thecatalyst particles free of metal contaminants. Metal contaminants in thepetroleum hydrocarbons undergoing treatment deposit on the catalyst andhave a harmful effect on the cracking reaction.

Practically all petroleum refineries have cracking units in which aportion of the heavier distillate is charged to the unit to increase theamount of gasoline and light fuel oil produced from each barrel of crudeoil. A popular system is the TCC system in which a granular catalyst ofabout 4-12 mesh Tyler size is gravitated as a compact mass throughreaction and regeneration zones. In the reactor the catalyst iscontacted with the petroleum oil heated to provide at least a highvolume of vapor and the conversion takes place during transfer throughthe voids in the bed. carbonaceous deposits are produced on the catalystduring reaction and hence spent catalyst is continuously transferred tothe regenerator and brought into contact with a large volume of air. Thecontaminant is burned from the catalyst whereby the catalyst is largelyrestored in activity.

Certain metals, such as iron, chromium, nickel and vanadium, are pickedup by the catalyst during usage in the system, primarily from thehydrocarbon charge. These metal contaminants are not removed during thenormal regeneration and tend to accumulate to a high level on thecatalyst. These metal impurities tend to produce more gas and cokeduring the cracking reaction and cause less gasoline to be produced. Forexample, it is reported (Oil and Gas Journal, vol. 57, No. 29, July 13,1959, at page 133) that for a fluid cracking catalyst the sum of thep.p.m. (parts per million) of iron plus 4 times the ppm. of copper, plus2 times the p.p.m. of vanadium, plus 9.2 times the ppm. of nickel in thehydrocarbon charged to the unit should not exceed about 4.0. Thus an oilthat contains 1.0 ppm. iron, 0.1 ppm. copper, 0.5 ppm. vanadium, and 0.3ppm. nickel would give a total of about 5.2 and this would indicaterapid contamination of fiuid type catalyst. Somewhat larger amounts ofcontaminants can catalytic systems, such as the TCC system, but in thiscase the nickel content of the catalyst should not exceed 100 ppm. andpreferably should not exceed about 60 ppm. without adversely affectingthe yield of the desired products.

It has been known that the metal contaminants concentrate on the outersurface or skin of the catalyst particles and that by removing the outersurface of the catalyst, the catalyst could be restored to its normalcondition. This surface concentration has been considered to be in alayer having a depth of 40-100 microns and that, therefore, the removalof a layer of that depth would be required to restore the catalyst.Various techniques have been proposed for removing the surface layer ofthe metal contaminated catalyst, such as the use of an abrasive particlecarried concurrently with the catalyst in a stream of gas, as disclosedin U.S. Patent No. 2,892,771. The US. Patent No. 2,421,212 proposesremoving particles below micron size from a fluidized system to'maintain higher average cracking ability. The

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be tolerated in moving bed 3,lh@,%8 Patented Dec. 15, 1964:

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US. Patent No. 2,651,600 proposes injecting streams of fiuid into afluidized catalyst system to provide increased attrition followed byremoval of particles less than 40 microns in size to eifect removal ofmetal contaminated catalyst. These systems have not been entirelysatisfactory, however, since they require the removal of an excessiveamount of catalyst to retain metal contamination to desired low levelsand furthermore involve an eX- cessive amount of breakage of thecatalyst particles which results in nonselective removal of catalystfrom the systern.

I have found that contrary to prior belief, the major concentration ofthe metal contaminants are located on a layer at most no more than about10 microns deep and largely less than about 5 microns deep. What isrequired is a method and means of removing a layer not 20, 40 or 60microns deep but actually a layer not over about 10 microns deep andgenerally not more than about 5 microns deep.

It is an object of this invention to provide a method and means ofremoving from a metal contaminated catalyst a fine outer layer ofmaterial containing a large proportion of the metal contaminants withoutremoving any substantial amount of the uncontaminated catalyst.

It is a further object of this invention to provide a method and meansfor removing from the metal contaminated catalyst of a cracking systemthe outer layer of the catalyst to a controlled depth required to removea large proportion of the metal contaminants without substantialcatalyst loss.

It is a further object of this invention to provide a method and meansof removing a layer of surface catalyst from a cracking catalyst in theform of dust of a particle size not greater than 2 microns.

It is a further object of this invention to provide a method andapparatus for removing a surface layer of cracking catalyst fromparticle-form cracking catalyst contaminated with metals as a dust of aparticle size less than about 1 micron diameter.

One aspect of this invention involves the transfer of metal contaminatedcatalyst particles to a reconditioning zone in which the particles aremaintained in the form of a bed in substantial touching contact butmaintained substantially weightless by the upward transfer of a gas orvapor through the mass. Mechanical movement is provided in the mass toeffect light continuous moving contact of one particle against otherparticles at a rate high enough to provide removal of particles of asize at least less than about 2 microns and primarily less than 1 micronin size. Reconditioned particles are removed from the reconditioningzone.

The invention will be disclosed more fully in the following detaileddiscussion as well as in the attached figures which are referred to inthis discussion.

FIGURE 1 shows a complete moving bed hydrocarbon conversion system inwhich the invention is incorporated.

FIGURE 2 shows a vertical view in section of the stirring apparatus ofthis invention.

FIGURE 3 shows a vertical view in section as seen on plate 3-3 of FIGURE2.

FIGURE 4 shows a plot of Nickel in Dust Removed, p.p.rn. versus DustRemoved (percent weight) and Shell Thickness (microns).

Referring now to FIGURE 1, the catalyst is gravitated as a compactcolumn through the conduit 10 into the reactor 11 and travels as acompact gravitating bed through the reactor in contact with thehydro-carbons undergoing reaction. These hydrocarbons are prepared fortreatment and introduced into the reactor through conduit 12. Theproducts are removed through the conduit 13 to further processingapparatus not shown. The temperature in the reactor is normally about900l000 F. and the pressure about -20 p.s.i. (gauge). The catalystaccumulates a carbonaceous deposit and this spent catalyst istransferred through the conduits 14 to the regenerator 15.

The catalyst gravitates as a compact mass through the regenerator 15 inwhich it contacts air which burns the carbonaceous material on thecatalyst. The air is introduced into the regeuerator through the conduit16 and is removed as flue gas through the conduits 1'7 and 18. Thetemperature in the regenerator ranges between about 10001400 F. and thepressure is usually about atmospheric pressure.

The regenerated catalyst is gravitated as compact streams through theconduits 19 into the lift pot 20. The catalyst contacts a stream of liftgas introduced into the lift pot through the conduit 21 and passesupwardly through the lift pipe 22 as a dilute phase flowing stream tothe separator 23. The lift gas is discharged from the separator 23through the conduit 24 and the separated catalyst is primarily returnedto the reactor 11 through the conduit 10.

Various contaminating metals, such as nickel and vanadium, areintroduced with the oil charge and deposit on the catalyst in thereactor 11. These metals are not removed by the combustion in theregenerator 15 and hence they build up to high levels of concentrationon the catalyst provided the catalyst remains in the system for asufiicient number of cycles. Early moving bed systems and catalyst usedin these systems caused a certain amount of attrition damage to thecatalyst, both in the catalytic section and in the lift section, whichkept the metals content on the catalyst from building up to too high alevel. In recent years gradual improvement of the system and catalysthave made it possible for the catalyst to remain in the system so longin undamaged condition that excessive levels of metal contamination arereached. This has necessitated removal of large amounts of usablecatalyst with replacement of this catalyst with fresh catalyst or torestrict the amount of heavy stocks which can be charged to the reactorsto maintain the metals content on the catalyst below safe operatinglimits. This is an exceedingly expensive and wasteful procedure. Suchhardened catalyst particles are fully disclosed in US. Patent No.2,900,349.

In this invention a side stream of the catalyst is taken from theseparator 23 through the conduit 25 to a reconditioner 26. Gas isintroduced into the reconditioner 26 from the conduit 27 and gas andfine particles are removed through conduit 28. The gas flow is adjustedto just remove the weight effect from the catalyst in the reconditioner26 while maintaining the reconditioner nearly full of catalyst as ahomogeneous mass. This permits catalyst movement readily but in constantcontact with other catalyst particles. A motor 40 is connected to ashaft 41 and this rotates a mechanical agitator in the reconditioner 26so that the catalyst particles are brought into continuous movingcontact with each other to effect removal of exceedingly small particlesof catalyst from the surface of the catalyst particles. These particlesare so fine that they readily escape with the su porting gas through theexit conduits. The rotating agitator must insure that substantially theentire mass of particles is in constant motion and continually renew thepoint of contact with other particles. For practical application theparticles must make a great many contacts per unit of time with eachother. The reconditioned catalyst is withdrawn through the conduit 42and returned to the lift pot 20 for reuse in the process.

In order to establish the optimum amount of surface to be removed, inremoving metal poison, and thus determine the maximum desirable dustparticle size, some experiments were made in which the extreme outersurface of the catalyst particles, or in this instance, catalystspherical beads, was removed by gently rolling the beads one year.

suspended in bottles of naphtha. In these experiments, after the beadswere rolled for a specific time, the removed surface material wascollected and the beads returned for additional increments of surfaceremoval. The catalyst beads used in these tests were newly developedcatalyst beads of unusual hardness and resistance to attrition (such asthose disclosed in US. Patent No. 2,900,349). These beads had been usedin a commercial TCC unit and had accumulated an average nickelconcentration of 45 p.p.m. nickel. The maximum nickel concentration wasfound in the first particles removed to be 7400 ppm. This correspondedto a shell thickness of only 0.005 micron or 0.001% weight of the bead.At 0.2 micron shell thickness or 0.4% weight of bead removal, the nickelconcentration was found to be about ppm. These values correspond to aratio of :1 at 0.005 micron shell thickness and 33:1 at 0.2 micron shellthickness, as compared with the average nickel content on the catalystbead. These tedious tests showed that removal of less than a 2% micronthickness shell of the catalyst would in fact remove a substantialportion of the metal contaminants and hence would be a practical methodof restoring the catalyst without substantial catalyst weight lossprovided the removal of such a fine layer could be accomplished on apractical basis. These tests were conducted on used catalyst in whichthe catalyst had been considerably penetrated by metal contaminants. Forfresh catalyst, adequate control can be obtained by removing an eventhinner layer, since the metals on the fresh catalyst do not penetrateas far into the catalyst. The results shown on curve 4 are for catalystswhich had been in commercial service for about In many instances, theremoval of a layer about 2 microns thick for new catalyst will,therefore, be adequate to maintain the catalyst in excellent operatingcondition.

Careful measurements conducted to determine the energy required to breakbeads and form new surfaces thereon showed that 5.5 foot pounds persquare foot of new surface was required. Using this figure it wasdetermined that 230,000 foot pounds would be required to produce onepound of catalyst dust of one micron size. Translating this tocommercial quantities, 1000 pounds of dust per day requires about 5horsepower input at 100% grinding efficiency. Using the 5.5 foot poundsper square foot energy figure for formation of new catalyst surfaces,the energy requirement to produce a one micron particle is 159 l0- footpounds. This energy corresponds to that obtained by dropping a singlesix mesh bead from a height of about 0.0008 millimeter. Since one poundof one micron dust represents 1.45 million billion particles, or that420 million particles are produced in removing 0.5% by weight from asingle bead, these early experiments showed that a grinding machine toaccomplish the desired thin layer removal would have to impart atremendous number of minute energy inputs to the beads. It wasconsequently considered necessary to develop a grinding device embodyingthe principle of limited freedom of movement of the beads, gentlemulti-million contact of bead with other beads, and removal of dust assoon as formed so that the dust does not coat the bead surface andprevent further grinding.

I found that a satisfactory grinding mechanism could be provided bymounting a stirring member vertically on a horizontal shaft in a chamberas shown on FIGURES 2 and 3 attached. The chamber 43 may be in the formof a box with a perforated floor 44 adapted to hold the catalystparticles or beads above the bottom 45 of the box. A gas, such as air,is introduced through the conduit 46 into the region 47. The gasdistributes uniformly through the apertures 43 in the perforated floor44, the pressure drop being adjusted to effect uniform gas distribution.The particles are supported by the upward flow of gas, the pressure dropbeing adjusted to substantially counterbalance the weight of thecatalyst in the box.

In other words, the pressure drop of air in pounds per square inch isjust equivalent to the weight of a column of the beads in the bed havinga cross section of one square inch. The upper limitation is that pointat which bubbles begin to form in the bed when the stirring mechanism isidle but which disappear when the stirring mecha-.

hing other particles. The stirring wheel 49 is located vertically withinthe catalyst mass on the horizontal shaft 50. This shaft projectsthrough the wall 51 of the box 43 and is driven at a moderate speedv bythe motor 52. The speed of the wheel will depend on the size of thewheel, roughness or shape, as related to its ability to maintain thebeads in rapid motion. The wheel disclosed has a hub with radial spokeswhich serve as stirring members when the wheel is rotated. The stirringwheel causes a movement in the catalyst bed, the particles tending toslowly follow the wheel. The particles contact the wheel surface but,what is more important, the particles are caused to make enumerablecontacts with each other. The gas flow through the bed is adjusted onlyto provide a supported bed and in this condition the particles cannotmove without rubbing adjacent particles. This movement provides theenergy transfer in the limited amount necessary to remove particles ofabout 1 micron or less. Where the bulk density of the particles is lessthan a substantially compact bed, such as in a boiling fluidized bed,the energy transfer is too great and catalyst breakage occurs, or atleast the particles formed are substantially greater than 1 micron insize. Where the gas how is less than that required to substantiallyfloat the particles, there is increased resistance to movement,excessive particle breakage occurs and the particles formed aresubstantially greater than 1 micron particles. With the particles justweightless, however, most of the particels formed are about 1 micron orless and these particles are so small that they are entrained in therising gas and removed with the gas as soon as formed. The gas and fineparticles leave through the apertures 53 in the cover plate 54 and arewithdrawn from the collection region 55 below the top cover 56 by theconduit 57.

EXAMPLE I As an illustration of the invention a box 4" wide, long, and12" high was filled to within about 2" of the top with catalyst beads. Agrinding wheel 4" to 6" in diameter was rotated in a vertical planelocated in the center of the box. Air was passed upwardly through the ofthe column of beads for a unit area in the box. The apparatus was foundnot particularly sensitive to air flow rate, a value 10% higher or lowerthan that required to just support the beads being operable. Unusualvariationi'rom this weight balancing flow rate was found, however, to beunsatisfactory, producing bead chipping and decreased grinding rate. Itwas also found that the grinding chamber should be filled by the beadsto a level substantially above the top of the wheel to prevent anysingle particle building up an excessive velocity before contact withother beads or vessel walls. The aim of this invention is accomplishedby a great number of very small energy transfers from catalyst head tocatalyst bead per unit of time. Most of these experiments were performedat an air rate yielding slight bubbling in the bed. When the wheel wasstarted, the bubbling disappeared and the beads slowly rotated in thesame direction as the wheel, with the beads possessing freedom ofmovement. Several types of wheels were tested in this apparatus and allgave satisfactory dust particles (0.5-1.5 microns) without chipping thebeads. The various wheels also gave about the same concentration ofmetal poisons in the dust; about 10 to 12 times that of the originalbeads. This concentration ratio is higher in a continuous system,through which the beads flow uniformly, as compared with the batchsystem described hereinabove. The data from these tests is shown in theattached FIGURE 4, being a plot of nickel concentration in the dust inppm. versus the dust removed as percent weight of the catalyst beads andshell thickness removed in microns. The grinding wheels tested were:

(1) A high density silicon carbide wheel impregnated with epoxy resin.

(2) A tungsten carbide grit wheel bonded with epoxy resin.

(3) A boron carbide grit wheel bonded with epoxy resin.

(4) A steel grit wheel, hard tempered, and bonded with epoxy resin.

(5) A wire brush wheel of 6" diameter fitted with 7 5 /2 in. diametersoft iron side plate.

(6) A corrugated steel Wheel, hard tempered, with concentriccorrugations (=66 Rockwell C).

(7) A soft iron wheel, made of 5 /2 in. diameter disc sheared from a 16gauge black iron sheet (60 Rockwell (8) A soft aluminum wheel, made of 5/2 in. diameter disc sheared from 16 gauge aluminum sheet.

(9) A hub and spoke wheel formed of two rows in staggered arrangementor" solid radially extending steel spokes set in the wheel hub. Thespokes were hard tempered (63 Rockwell C) and were arranged 6 in eachrow.

The performance of these wheels is shown in the folbed of heads at aflow rate just sufiicient to counteract lowing Table I:

Table I PERFORMANCES OF VARIOUS GRINDING WHEELS (STIRRING DEVICES)Grinding Pounds of Wheel Rate, lbs. Dust Type of Wheel D1a., R.P.M. perday Produced Remarks Inches per ft. 2 of per Pound Grindin g Wheel LossSurface Silicon Carbide Epoxy Basin Impregnatcd i. 6 1,250 13 210 Steelrims on wheel to prevent chipping. TlfilgStGll Carbide Grit Bonded withEpoxy 4 2, 460 33 450 Grit appeared to crumble rather than wear.

csm. Boron Carbide Grit BondedEpoxy with Resin... 4 3, 550 13 20 Gritappeared to be brittle. Steel Grit Bonded with Epoxy Resin 4 2, 460 16400 Grit developed polished surface. Wire Brush Wheel with Side Plated 61,240 23 340 These results are based on peripheral area. CorrugatedHard-Temper Steel Wheel 4 2, 470 7 550 Corrugation ridges developedpolished surface. Soft Iron Disc- 5% 2, 450 15 28 Disc developed a 4micron roughness. Soft Aluminum D sc 5% 2, 440 30 10 Disc developedradial wear grooves. Hub and Spokes, Hard-Temper Steel Spok 5 1, 250 1637, 500 Spokes acquired highly polished surface.

the force of gravity and essentially float the beads. The pressure dropof the air was just equivalent to the weight From this Table I it can beseen that the grinding rate varied considerably for the differentwheels. The grinding rate could have been made the same for thedifferent wheels by adjusting the speeds of rotation. It is seen thatthere was an extremely wide difference in the amount of dust producedper pound of wheel loss. Wheels constructed of hardened steels,

particularly the hub and have been tabulated in Table III as follows 8The grinding efliciencies of the different types of grinding wheelstested were determined and the particle size was calculated and observedin actual test, both optically and by use of the electron microscope.These results Table III ENERGY RE QUIREMENTS AND WHEEL EFFICIENOIES FORGRINDING HARD BEAD CATALYST OF ABOUT C S MESH SIZE Power, Foot poundsper minute Grinding Etn- Pounds of ciency, Percent Energy Consumed Exp.Dust (Power to produce per Pound of Dust, Calculated Observed b N o.Produced Delivered to Converted to Consumed to new surface+powerft.-lbs./lb. (does Dust Particle Dust Particle Per Hour Grinding Heat byProduce New delivered to not include Size, Microns Size, Microus WheelFriction Surface (by grinding wheel) frictional energy) difi'crence)WIRE BRUSH WHEEL 1 0.32 7, 000 4, 600 2, 400 34 450, 000 0. 51 From 0.2to 1.0 2 O. 24 7, 860 5, 540 2. 320 30 583, 000 0.39 micron averag- 30.21 7, 350 5, 000 2, 350 32 672,000 0.34 ing 0. 5 micron. 4 0. 22 7,260 0, 250 l, 010 14 275, 000 0.83 5 0.32 6, 780 4, 600 2, 180 32 409,000 0. 56 6 0. 29 6, 700 4, G00 2, 100 31 431, 000 0. 53

SOFT IRON DISC WHEEL 1 0.24 3, 980 3, 540 440 11 110, 000 2. 1 Averageabout 2 0. 11 6, 850 2, 030 3, 920 57 2, 150, 000 0. l1 0.6-0.8 micron.3 0. 17 4, 440 3, 450 990 22 348, 000 0. 66 4 0. l, 910 1, 190 720 37428, 000 0. 54

HUB AND SPOKE WHEEL" 1- 0. 71 4, 200 3, 370 830 70, 000 3. 3 Averageabout 2 0. 69 4, 200 3, 190 1, 010 24 88, 000 2. 6 0.6-0.8 micron.

)tion of 5.5 lt.-lbs./lt. icroseope observations.

spoke wheel, gave very high dust makes per pound of 11 Based on anenergy consum; b From optical and electron m wheel loss, whereas wheelsconstructed of commercial grinding materials were less satisfactory, butnevertheless acceptable. While the soft iron wheels wore rapidly, therapid wear is largely offset by the low cost of those wheels as comparedto the hardened steel or commercial grinding materials. While theinvention has been disclosed by the use of stirring wheels mounted in avertical plane on a horizontal axis, good results can also be obtainedwith the stirring device mounted in other than a vertical'plane.

As the.r.p.m. of the grinding wheel is increased the amount of dustproduced is increased but generally this is obtained at a reduced amountof dust per pound of wheel lost. Tests conducted at different r.p.m.using 50 of new surface as determined in bead breakage experiments.

Based on the data of Table III the dust produced by any of these wheelsis seen to be of the order of 0.5 micron diameter. The energy input tothe grinding wheels is seen to range from about 400,000 foot pounds perpound of dust for the Hub and Spoke Wheel to about 1,500,000 foot poundsper pound of dust for the Wire Brush Wheel and Soft Iron Disc Wheel.These energy inputs correspond to a 10 to 30 horsepower machine to make1,000 pounds of dust per day.

While a single grinding wheel has been shown to be used in demonstratingthe invention it is obvious that several wheels in parallel can be usedsuccessfully and that these would provide the increased capacity desiredin large operations. Such an arrangement is contemplated as within thescope of this invention. In a commercial application of the invention afew tons per hour of the catalyst beads are passed through a grindingzone Table H as a slip stream from the main catalyst stream tocontinuously remove no more than about one percent and G generally up toabout one-half of one percent weight of rindmg it t. of Rate, Du st Perthe beads as dust of a particle size at least less than 2 Wheel egg?microns diameter and preferably less than 1 micron diame- LOSS ter. Thegrinder may suitably be a box of about 10 to 20 sq. ft. cross sectionwith a shaft extending through the Sollcon Carbide Wheel 1 box andcarrying a gang of grinding wheels. The catalyst Tungsten Carbide withEpoxy 11275 28 820 beads are introduced at one end of the box andremoved R051 2%? 2 from the other end for return to the main cycliccatalyst 50mm, wheel 3g 53 stream. Gas introduced to the bottom of thebox is at a controlled flow rate to ust float the beads without ex-Catalyst beads take up moisture when in contact with atmospheric air inamounts of about 1-5% of the weight of the beads. The catalyst particleslose this moisture when heated to high levels. In order to test theaffect of moisture in grinding the surface of catalyst beads, tests wereconducted using beads dried at about 900 F. The results showed thatdrying the beads prior to grinding the surface did not affect either thegrinding rate of the beads or the ratio of dust produced to the weightof wheel loss.

therefore useful in removing surface layers from catalyst of the fluidtype. The invention can be used to grind ball bearings, there being nolimit on the size of particle or density of particle undergoingtreatment. Irregular particles are rounded by treatment according tothis invention. Even if the material being treated is soft, theinvention can still be used because the material is not treated roughly.Hence a polishing treatment can be given pearls or similar articles bythis invention. The invention has been disclosed hereinabove withrespect to particular apparatus and tests conducted with this apparatusfor purposes of illustration. The invention is not intended to belimited by this description but only by the attached claims.

This case is a divisional application of case Serial Number 851,870,filed November 9, 1959, now Patent Number 3,060,117.

I claim:

1. The method of grinding a thin layer up to about 10 microns thicknessfrom solid granular particles which comprises maintaining a mass ofsolid granular particles in the range of from about 4 to 12 mesh size ina treating zone, passing a gas upwardly through the mass of granularparticles at a velocity below fiuidizing velocity of the introducedparticles but sufficient to aerate the mass of particles, effectingabrasion of particle surface to a desired depth by rotating a mechanicaldevice at a high rpm. in the mass of particles and removing abradedparticles from said mass of solid granular particles as rapidly asformed with said gas.

2. The method of removing a thin surface layer from a solid granularparticle which comprises introducing solid granular particles into atreating zone in an amount sufficient to provide a bed of particles,aerating the bed of particles with an aeration gas in an amountsufiicient to remove from the bed surface material abraded from thesolid particles, moving the bed of particles generally horizontallythrough the treating zone and abrading material from the surface of thesolid particles by high speed rotation of an abrading member submergedwithin the bed of particles.

3. The method of removing metal contaminates from the surface of agranular particle of catalyst which coinprises passing an aerated bed ofmetal contaminated granular catalyst particles through a horizontalabrading zone containing a solid abrading member rotating at a high rpm.

4. The method of removing the surface from particles in the range offrom about 4 to 12 mesh size which comprises maintaining a bed of thesolid particle material in a treating zone, passing an aerating gasupwardly through the bed of particles below fluidizing velocity ofparticles in the 4 to 12 mesh size range, abrading the surface of theparticles in the bed with a plurality of rapidly rotating abradingmembers and removing particles less than 12 mesh size substantially asrapidly as formed from said bed with said aerating gas.

References ited in the file of this patent UNITED STATES PATENTS1,647,249 Podszus Nov. 1, 1927 1,930,683 Kramer Oct. 17, 1933 2,421,212Medlin May 27, 1947 2,651,600 Tait et al. Sept. 8, 1953 2,826,011 RiveraMar. 11, 1958 2,892,771 Milliken June 30, 1959 UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent No. 3,160,998 December 15, 1964John W. Payne It is hereby certified that error appears in the abovenumbered patent requiring correction and that the said Letters Patentshould read as corrected below Column 2, after line 30, insert thefollowing paragraph:

It is a further object of this invention to subject catalyst containingcontaminant metals to a reconditioning treatment to effectively reducethe metal content without substantial catalyst loss.

column 4, line 14, for "0.4%" read 0.04% line 16, for "150" read 1500columns 5 and 6, Table I, first column, line 4 thereof, for "Epoxy withResin" read with Epoxy Resin Signed and sealed this 3rd day of August1965. (SEAL) Attest:

ERNEST W. SWIDE'R EDWARD J. BRENNER Attcsting Officer Commissioner ofPatents

3. THE METHOD OF REMOVING METAL CONTAMINATES FROM THE SURFACE OF AGRANULAR PARTICLE OF CATALYST WHICH COMPRISES PASSING AN AERATED BED OFMETAL CONTAMINATED GRANULAR CATALYST PARTICLES THROUGH A HORIZONTALABRADING